In recent years, transmitting devices (hereinafter referred to also as nodes) compatible with an optical transmission network (optical transport network (OTN)) or the like have been provided as transmitting devices for carriers. In addition, the technology of a two-way ring network is known, the two-way ring network being formed by coupling a plurality of transmitting devices in the form of a ring in an optical transmission network allowing communication to be performed bidirectionally.
A transmitting device coupled to such a two-way ring network is coupled to a first route and a second route as communication paths on the two-way ring network. For example, the transmitting device branches signal light received from the first route into two pieces of signal light by using a 1×2 optical coupler that branches one piece of signal light into two pieces of signal light. In addition, the transmitting device terminates and outputs one of the branched pieces of signal light, and distributes the other piece of signal light to the second route. Then, by using a 2×1 WSS (wavelength selective switch) that multiplexes two pieces of signal light into one piece of signal light, the transmitting device multiplexes the signal light distributed to the second route and signal light to be transmitted to another transmitting device, and outputs the multiplexed signal light to the second route.
Here, when the optical transmission network is expanded by coupling the two-way ring network and another optical transmission network to each other, a transmitting device serving as a hub for each of the networks (which transmitting device will hereinafter be referred to also as a hub node) distributes signal light received from one of routes to all of the other routes. For example, a hub node coupled to two two-way ring networks is coupled to a first route and a second route as communication paths on one two-way ring network, and is coupled to a third route and a fourth route as communication paths on the other two-way ring network.
Such a hub node branches signal light received from the first route into four pieces of signal light by using a 1×4 optical coupler that branches one piece of signal light into four pieces of signal light. Then, the hub node terminates and outputs one of the branched pieces of signal light, and distributes the three remaining pieces of signal light to the second route, the third route, and the fourth route.
Similarly, the hub node branches each of pieces of signal light received from the second route, the third route, and the fourth route into four pieces of signal light, and terminates one of the branched pieces of signal light and distributes the three remaining pieces of signal light to the routes different from the route from which the signal light is received. Then, by using a 4×1 WSS that multiplexes four pieces of signal light into one piece of signal light, for example, the hub node multiplexes the three pieces of signal light distributed from the second route, the third route, and the fourth route to the first route and signal light to be transmitted to another transmitting device, and outputs the multiplexed signal light to the first route.
However, the above-described technology needs optical couplers and WSSs having a large number of ports because destinations to which signal light is branched are increased as the optical transmission network is expanded. As a result, for example, cost involved in expanding the optical transmission network is increased.
The followings are reference documents.
[Document 1] Japanese Laid-open Patent Publication No. 2006-087062 and
[Document 2] Japanese Laid-open Patent Publication No. 2010-283446.